Firstly, the tank specs: 1. 2 gallon bowl.
2. Ammonia level was ~3.
3. Freshwater.
4. Had just done a full water change before the onset of fin loss.
5. I have one Betta Splenden. Have had it for several months now.
6. Has not been quarantined, but has been moved to larger tank.
7. Temperature is almost always at ~80 degrees.
8. No live plants.
9. No filter in bowl.
10. Flat mini heater placed under the gravel was the only equipment in bowl.
11. The bowl was in the corner of my room against the same wall as the only window, so sunlight would never hit it directly throughout the day.
12. I had done a complete water change about a week or so ago. It was the next day I noticed the fin deterioration.
13. My fish is fed TetraBetta Floating Mini Pellets and freeze-dried blood worms. Usually fed once a day after I wake up.
14. Soon after a full water change I noticed the tail fins had become jagged and considerably shorter.
15. No treatments.

Today, Feb 15, I moved my betta, Roy Cherry, into a new 10 gallon tank in hopes of eliminating any prior water conditions he was living in. I've also installed a Tetra Whisper In-Tank Filter to maintain clean water conditions. Pictures below of poor Roy as of today :< http://i50.tinypic.com/ounn5u.jpghttp://i45.tinypic.com/x0xqav.jpg

About a week ago, when Roy was still living in his 2 gallon bowl, I noticed severe fin deterioration the day after I'd done a complete water change. This marks the first time I've noticed any health decline in the 2-3 months I've had him. A worker at Petco told me today that it could be the ammonia levels and to treat that before possible fin rot, so I purchased a Jungle Brand Ammonia Quick Dip testing kit and sure enough, the ammonia reading was about a 3. It was after this reading that I prepared the newly purchased 10 gallon tank and transitioned Roy into it. But were high ammonia levels the only problem?

I guess what I'm wondering is if any of you are able to recognize from the above pictures what exactly is happening with Roy's fins and what I am able to do about it. I don't have the background to distinguish between fungal and / or bacterial fin rot. Or Ammonia poisoning? Should I move him back to the 2 gallon bowl in an effort to quarantine and medicate him, or can he be medicated in the 10 gallon tank, if need be at all?

How often were you cleaning his 2 gallon? 3ppm is ridiculously high... I'm surprised your fish is still alive frankly.

To me it sounds like you unintentionally cycled his 2g because of infrequent cleaning. Then when you cleaned it for the first time in a few weeks you killed all the ammonia-eating bacteria and poof, nobody's around to eat the ammonia so it skyrockets.

For once a petco employee actually gave you decent advice. If you take care of the ammonia he should heal up beautifully without any medications.

Mm, thank you Kelly. I've done a bit of reading up on tank cycling as I never quite understood it before, and what you said makes perfect sense, and provides a clear explanation for the problem. Thank you for your input.

With the 10 gallon tank now, along with the gravel vacuum and much more broad tank opening, filter, etc., water changes and typical maintenance should be much easier, and I hope for a full recovery soon.

As well, I have planted live plant bulbs under the gravel to grow and provide natural filtration.